1. Field of the Invention
The present invention relates to techniques for printing using an inkjet head.
2. Description of the Background Art
Conventionally, a printing apparatus which includes a head with a plurality of outlets and controls ejection of a fine droplet (which will hereinafter be simply referred to as a “droplet”) of ink from each of the plurality of outlets while scanning the head relative to a printing paper, has been employed. Also, as one modification of the above-noted printing apparatus, an apparatus of a type that includes a plurality of heads which are placed to cause numerous outlets to be arranged in a direction perpendicular to a scanning direction in a range corresponding to a width of a printing paper (in other words, includes full-line heads), is known. The apparatus of the foregoing type can perform a printing process at a high speed through one scanning operation on a printing paper using the heads (in other words, in one pass).
Japanese Patent Application Laid-Open No. 2003-266651 (which will hereinafter be referred to as “Reference 1”) discloses that when a travel speed of a head is lower than a reference speed, a droplet of ink is ejected at a time behind a time when a droplet of ink is supposed to be ejected if the head moves at the reference speed, to thereby accomplish printing with high accuracy. On the other hand, according to Japanese Patent Application Laid-Open No. 2001-191591 (which will hereinafter be referred to as “Reference 2”), one of plural print speeds is selected and set by monitoring an amount of writing data which is input from the outside and stored in a print buffer, to thereby accomplish printing at an optimal print speed which is suitable to an amount of writing data stored in the print buffer.
In the meantime, an inkjet head performs an operation related to ejection of droplets of ink from a plurality of outlets in response to input of a driving signal generated based on writing data. In this regard, a basic time period with which the driving signal is input (or a driving frequency) is fixed as a rated value of the head, typically. Then, the head ejects droplets or performs a non-ejecting operation (operation when ejection of droplets is not performed) such as an oscillatory motion which is so slight that a droplet cannot be ejected from each outlet, with a basic time period. In this manner, the head properly and reliably achieves ejection of ink from the outlets while keeping a state of the vicinity of each outlet of the head substantially unchanged. However, in a printing apparatus including the foregoing head, when a printing process is performed with a travel speed of the head relative to a printing paper being reduced to be lower than a steady speed determined in accordance with a basic time period as in References 1 and 2, an operation related to ejection of droplets from the outlets is repeated with a longer time period than the basic time period. As a result, the state of the vicinity of each outlet of the head is changed or somewhat affected, to fail to reliably and properly eject ink in some cases.